Circuit board and a method for making the same

ABSTRACT

A method for making multi-layer electronic circuit boards  64  having “blind” type apertures  28, 30  which may be selectively and electrically grounded and further having selectively formed air bridges and/or crossover circuits  45, 46.

(1) FIELD OF THE INVENTION

[0001] The present invention relates to a circuit board and to a methodfor making a circuit board and, more particularly, to a multi-layercircuit board and to a method for making a multi-layer electricalcircuit board having air-bridges and/or crossover circuits and furtherhaving metallized apertures which are selectively formed through theboard and which may be selectively connected and/or detached and/orisolated from an electrical ground plane.

(2) BACKGROUND OF THE INVENTION

[0002] Multi-layer circuit boards allow electrical components toselectively and operatively populate opposed surfaces of each board (orother respective interior portions of each of the boards), therebydesirably allowing each of the electrical circuit boards to contain arelatively large amount of electrical components which efficiently anddensely populate the respective boards. It is desirable to allow each ofthe component-containing surfaces or portions of a created and/or formedelectrical circuit board to communicate and/or be selectivelyinterconnected, thereby allowing the contained electrical components tocooperatively and selectively form one or more desired electricalcircuits. This desired communication and/or interconnection typicallyrequires the use of shared electrical ground planes, the transmittal ofpower and/or control type signals between each of the componentcontaining surfaces or board portions, and/or the connection and/orinterconnection of the various contained electrical components.

[0003] This desired interconnection typically requires that one or moreholes be drilled through each of the circuit boards, thereby physicallycreating at least one “through hole” or “via” lying between each of theopposed component containing surfaces and through the various interiorcircuit board portions. Such drilling is undesirable since it isrelatively time consuming, costly, potentially causes damage tosignificant numbers of the formed electrical circuit boards requiringthese circuit boards to be destroyed, and requires costly andinefficient electroless and/or electrolytic plating of the formed holesor “vias”.

[0004] While some attempts have been made to obviate the need for suchplating, such as by the use of a conductive epoxy within each of thedrilled holes, these attempts have not produced reliable electricalinterconnections and these produced interconnections are not typicallyadapted to allow the communication of electrical power signals betweenthe board surfaces or to securely and reliably allow the formed apertureto securely receive a component.

[0005] Further, it is desirable to form “air-bridges” or “crossover typecircuits” upon one or more selected surfaces and/or within certaincomponent containing portions of the formed circuit board in order toallow multiple levels of circuits and/or electrical interconnections tobe formed upon a single board surface or within a certain componentcontaining portion of the circuit board, thereby desirably increasingthe amount of electrical circuits which may be created upon and/orwithin the created circuit board.

[0006] These air-bridges or crossover circuits are typically formed byrather complicated, costly, and time consuming processes which requiresuccessive layers of material to be accurately and precisely aligned bythe use of rather complex and inefficient alignment processes and/ormethodologies. This alignment process is both time consuming and costly,thereby limiting and/or reducing the desirability of creating theseair-bridges or crossover circuits. Further, the formed bridges andcrossover circuits do not typically and efficiently accommodate certaindesirable circuit board interconnection processes and/or schemes such asand without limitation, the use of relatively heavy wire bonding (e.g.,using aluminum wire having a diameter of about five to about twentymilli-meters) or the direct connection of components to a surface of theboard.

[0007] There is therefore a need to provide a method for producing amulti-layer electrical circuit board which overcomes some or all of thepreviously delineated drawbacks, which selectively allows grounded andnon-ground “vias” and/or “through holes” to be desirably and selectivelyformed, and which further allows for the efficient and selectiveformation of air-bridge members or crossover members which desirablyaccommodate diverse types of circuit interconnection processes and/orschemes.

SUMMARY OF THE INVENTION

[0008] It is a first object of the present invention to provide a methodfor producing a multi-layer electrical circuit board which overcomessome or all of the previously delineated drawbacks of prior multi-layerelectrical circuit board forming methodologies and techniques.

[0009] It is a second object of the invention to provide a method forproducing a multi-layer electrical circuit board which overcomes some orall of the previously delineated drawbacks of prior multi-layerelectrical circuit board forming methodologies and techniques, whichallows for the selective, efficient, and reliable formation of metalizedapertures which cooperatively allow for communication by and betweenand/or interconnection of these various electronic components, and whichallows these apertures to be selectively created and/or formed withoutdrilling, and which allows these apertures to selectively, securely, andreliably receive a component and/or an element.

[0010] It is a third object of the invention to provide a method forproducing a multi-layer electrical circuit board which overcomes some orall of the previously delineated drawbacks of prior multi-layerelectrical circuit board forming methodologies and techniques and whichallows for the selective formation of metalized apertures which may beselectively connected or disconnected and/or isolated from a selectivelyformed electrical ground plane or bus.

[0011] It is a fourth object of the invention to provide a method forproducing a multi-layer electrical circuit board which overcomes some orall of the previously delineated drawbacks of prior multi-layerelectrical circuit board forming methodologies and techniques and whichallows for the selective and efficient formation of air bridges and/orcrossover members which are adapted to accommodate a wide variety ofcomponent interconnection assemblies.

[0012] It is a fifth object of the invention to provide a method forproducing a multi-layer electrical circuit board which overcomes some orall of the previously delineated drawbacks of prior multi-layerelectrical circuit board forming methodologies and techniques and whichallows the created circuit board to be functionally tested prior toreceiving the electronic components.

[0013] It is a sixth object of the invention to provide a method forproducing a multi-layer electrical circuit board which overcomes some orall of the previously delineated disadvantages of prior multi-layerelectrical circuit boards and which allows the various layers of theproduced circuit board to be relatively easily and desirably alignedwith other layers and/or with the circuit board before they arerespectively attached to these other layers and/or to the circuit board.

[0014] According to a first aspect of the present invention, a methodfor making an electric circuit board is provided. The method includesthe steps of providing a member having a central layer of a firstmaterial which is operatively positioned between first and second layersof a second material; placing a layer of a third material upon certainportions of the first layer, thereby exposing at least one portion ofthe first layer; placing a plurality of layers of the second material ontop of the layer of the third material, effective to form a multi-layerelectrical circuit board having an aperture which extends through theformed electrical circuit board and which terminates upon the exposed atleast one portion of the top layer.

[0015] According to a second aspect of the present invention amulti-layer circuit board is provided. The method includes the steps ofproviding a member having a central layer of a first material which isoperatively positioned between top and bottom layers of a secondmaterial; removing a portion of the first and the second layers, therebyexposing portions of the central layer of the first material; providinga first layer of a dielectric material and placing the provided firstlayer of the dielectric material onto certain portions of the top layer,thereby overlaying the exposed portions of the central layer andcreating first and second exposed portions of the top layer; providing athird layer of the second material and placing the third layer onto thefirst layer of the dielectric material and over the first and secondexposed portions of the top layer; removing those portions of the thirdlayer which overlay the first and the second exposed portions of the toplayer; providing a second layer of the dielectric material and placingthe second layer of the dielectric material onto the third layer afterthose portions of the third layer which overlay the first and secondexposed portions of the top layer have been removed; providing a fourthlayer of the second material and placing the fourth layer upon thesecond layer of the dielectric material and over the first and secondexposed portions of the top layer; and removing those portions of thefourth layer which overlay the first and the second exposed portions ofthe top layer, thereby creating an electrical circuit board having afirst aperture which extends through the third and fourth layers of thesecond material and through the first and second layers of thedielectric material while terminating within the first layer of thesecond material, and a second aperture which extends through the thirdand fourth layers of the second material and through the first andsecond layers of the dielectric material while terminating within thefirst layer of the second material.

[0016] According to a third aspect of the present invention, a circuitassembly is provided. The circuit assembly is made by the process ofproviding a core member having a central layer of a first material whichis operatively contained between a top and a bottom layer ofelectrically conductive material; creating an registration slot withinthe core member; placing dielectric material on certain portions of thetop layer, thereby exposing a first and a second portion of the toplayer, thereby creating a pre-circuit assembly; and using the createdregistration slot to selectively add layers of electrically conductivematerial to the pre-circuit assembly, thereby creating a circuitassembly having a first aperture which is formed through the createdcircuit assembly and which terminates within the first exposed portionand having a second aperture which is formed through the created circuitassembly and which terminates within the second exposed portion.

[0017] These and other objects, aspects, and advantages of the presentinvention will become apparent upon reading the following detaileddescription in combination with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIGS. 1(a)-(k) are successive sectional side views of amulti-layer circuit board being produced and/or formed in accordancewith the teachings of the preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

[0019] Referring now to FIGS. 1(a)-(k), there is shown a process 10 formaking a multi-layer electrical circuit board according to the teachingsof the preferred embodiment of the invention. As shown best in FIG.1(a), process 10 begins with the use and/or acquisition and/or formationof a member 12 having substantially identical first and second layers14, 16 which are formed from substantially identical electricallyconductive material. In one non-limiting embodiment of the invention,layers 14, 16 are formed from a commercially available electricallyconductive metal, such as copper. Member 12 further has a central layer18 which is positioned and/or “sandwiched” and/or operatively coupledbetween and to layers 14, 16 and which, in one non-limiting embodiment,comprises commercially available aluminum. Hence, in one non-limitingembodiment, member 12 comprises a double-sided copper clad aluminummember. In one non-limiting embodiment of the invention, a registrationslot or aperture 20 is formed within and through member 12 and is usedto relatively efficiently and easily allow successive layers of materialto be operatively coupled to the member 12 in a desired alignment and/orpattern. Particularly, aperture 20 may be formed in virtually anydesired shape and/or size desired by the user of the process 10 and isnot limited by the exact shape or size shown in FIG. 1(a). Alignmentslot 20 may be formed by known etching or other material removalprocesses.

[0020] In the second step of process 10, as shown best in FIG. 1(b),pre-determined portions of the layers 14, 16 are removed by aconventional pattern etching process. In one non-limiting embodiment,the etching process utilizes a commercially available “dry film” and/ora screen printed etch resistant material to protect those portions oflayers 14, 16 which are not to be removed, thereby allowing the material14, 16 to be selectively notched in the manner shown. The remainingportions 22 of the layers 14, 16, in one non-limiting embodiment, arecoated with and/or receive a layer of conventional tin 24 in order tosubstantially ensure that these portions 22 will not be further etched,removed, and/or reduced in the remaining steps of process 10. Thisetching/removal process causes certain apertures 25 to be created inlayers 14, 16, thereby exposing certain portions of central or coremember 18 and producing a pre-circuit assembly 17.

[0021] In the third step of process 10, as shown best in FIG. 1(c), aconventional and commercially available dielectric material 26 is placedupon certain portions of the layer 14 and the core member 18 by the useof alignment slot 20. Particularly, in this non-limiting embodiment, a“pre-punched” or pre-formed “sighting window” 29 is created in thedielectric material 26. This sighting window 29 may be of virtually anysize or shape and is relatively easily and visually aligned with theslotted aperture 20, thereby allowing the dielectric material 26 to bedesirably and operatively placed upon the predetermined portions oflayer 14 in a desired position and/or location, by the use of aconventional printing process such as a screen printing process or a dryfilm printing process. Similarly, in this non-limiting embodiment, allother layers of material which are operatively added to the circuitassembly, as shown in the remaining FIGS. 1(d)-1(k), also include suchpre-formed sighting windows 29 which allow these respective layers ofmaterial to be easily and operatively aligned with layer 14 and member12 in the manner which is shown and by use of the aperture 20.

[0022] The dielectric material 26 is made to fill apertures 25, whilecreating a first and a second apertures 28, 30 which terminate withinand/or upon respectively exposed regions or portions of layer 14. Aswill be seen below, these apertures 28, 30 are selectively extendedand/or lengthened and form “blind” or “non-through hole” type “vias” orapertures in the produced and/or created circuit assembly or board. Inone non-limiting embodiment of the invention, the dielectric material 26is partially cured in order for the material 26 to function and/or toserve as an adhesive in the next step of the process 10. Thus, the thirdstep of process 10 causes pre-circuit assembly 27 to be created.

[0023] In the fourth step of process 10, which is shown in FIG. 1(d), athird layer of electrically conductive material 32 is operatively andadhesively placed (i.e., laminated) onto the partially cured dielectricmaterial 26 and over the apertures 28, 30, thereby creating a thirdpre-circuit assembly 33. In one non-limiting embodiment, the third layerof electrically conductive material 32 is formed from conventional andcommercially available copper and is substantially identical to thefirst and second layers 14, 16.

[0024] In the fifth step of process 10, which is shown in FIG. 1(e), theportions 34, 36 of layer 32 which respectively reside over thepreviously created apertures 28, 30 are removed by a conventionaletching and removal process. The remaining portions of the thirdmaterial layer 32 are, in one non-limiting embodiment, coated and/orreceive commercially available tin 38 in order to substantially preventthese remaining portions from being further etched, reduced, and/orremoved, thereby creating a fourth pre-circuit assembly 35.

[0025] Further, in one non-limiting embodiment, the third layer ofelectrically conductive material 32 serves and/or functions as anelectrical ground plane and aperture 37, which is formed in this thirdlayer of electrically conductive material 32, communicates with thepreviously formed aperture 30 and extends the aperture 30 through theformed pre-circuit assembly. The extended aperture 30 is “disconnected”from electrical ground potential (i.e. the surface boundary 9 whichforms and surrounds the aperture 37 and the extended aperture 30 isphysically and electrically “disconnected” from the remaining portion ofmaterial 32) in order to later allow for the formation of a“non-grounded via” or “non-grounded aperture” in a manner which isdelineated below.

[0026] Similarly, aperture 39, which is formed in this third layer ofelectrically conductive material 32, communicates with the previouslyformed aperture 28 and extends the aperture 28 through the formedpre-circuit assembly. The extended aperture 28 is a “grounded via” or“grounded aperture” since the material boundary 11 which forms orsurrounds the extended aperture 28 remains physically and electricallyconnected to the remaining portions of this third layer of material 32.Extended apertures 28, 30 are each “blind” or “non-through hole” typeapertures or openings. In other non-limiting embodiments of theinvention, portions of material layer 32 may selectively overlay or“hang over” certain predetermined portions of the apertures 28, 30 inorder to cause the created and extended apertures 28, 30 to be formed ina certain desired shape or size. As will be seen later, extendedapertures 28, 30 are selectively filled with solder paste or some othermaterial. Hence, in these non-limiting embodiments, the overhangingportions of material layer 32 function as a “lip” or a “diving board” 41to retain the solder paste or material within the extended apertures 28,30.

[0027] In the sixth step of process 10, as shown best in FIG. 1(f), afifth pre-circuit assembly 49 is created. Particularly, a second layerof commercially available dielectric material 40 is placed onto theremaining portions of the third layer of electrically conductivematerial 32 by a conventional printing process, thereby furtherextending the respective length of apertures 28, 30. The dielectricmaterial 40 may again be partially cured in order to operatively andeffectively adhere to a layer of material which it supportivelyreceives. In the seventh step of process 10, as shown best in FIG. 1(g),a fourth layer of electrically conductive material 42 is placed onto andoperatively secured to (i.e., laminated onto) the dielectric material 40and over the extended apertures 28, 30. In one non-limiting embodimentof the invention, material 42 comprises commercially available copperand/or is substantially similar to the first, second, and third layersof electrically conductive material 14, 16, and 32. Hence, a sixthpre-circuit assembly 51 is formed in this seventh process step.

[0028] In the eighth step of process 10, as shown best in FIG. 1(h), aseventh pre-circuit assembly 59 is formed. Particularly, portions of thefourth layer of conductive material 42 are removed by a conventionalpattern etching and removal process, thereby removing those portions ofmaterial 42 which overlay extended apertures 28, 30 and furtherextending the length of “blind type” apertures 28, 30. As before, someof the layer of material 42, such as “diving board” portion 43, mayextend over these recently extended apertures 28, 30 in order to causethe apertures 28, 30 to be formed in a desired shape and/or tosubstantially ensure that the material which is placed within theseapertures 37, 39 remains securely intact. A layer of commerciallyavailable tin 44 is, in one non-limiting embodiment, attached to theremaining portions of material 42 in order to prevent these remainingportions from being further etched, removed, and/or reduced.

[0029] It should be realized that the additional and alternative layersof a dielectric material and an electrical conductive material may beoperatively attached to the pre-circuit assembly 59 in the foregoingmanner, thereby increasing the density of the assembly 59 and extendingor selectively lengthening “blind type” apertures 28, 30 through theseadditional layers. Additionally, it should be apparent that this process10 is adapted to allow a circuit board assembly to be created having aselected number of electrically conductive layers which are eachseparated by a dielectric material. Hence, while the first eight stepsof process 10 allow for the creation of two additional electricallyconductive layers 32, 42 upon member 12, additional electricallyconductive layers may be selectively utilized and created, therebyallowing a great variety of dissimilar multi-layer electrical circuitboards to be produced by process 10.

[0030] In the ninth step of process 10, as shown best in FIG. 1(i), aneighth pre-circuit assembly 60 is created. Specifically, portions of thecentral layer 18 are removed by a conventional controlled etchingprocess, thereby creating and/or producing electrically conductiveair-bridges 46 within and/or by the use of material layer 16.

[0031] In the tenth step of process 10, which is shown best in FIG.1(j), a ninth pre-circuit assembly 62 is created by selectively placingcommercially available screen print type solder paste 48 within each ofthe created “vias” or apertures 28, 30. Particularly, as best shown inFIGS. 1(i) and 1(j), “blind” type aperture or “via” 28 begins at and/orwithin the first conductive layer 14 and extends through the first layerof dielectric material 26, the third layer of conductive material 32,the second layer of dielectric material 40, and the fourth layer ofconductive material 42. Similarly, “blind type” aperture or “via” 30begins at and/or within the first conductive layer 14 and extendsthrough the first layer of dielectric material 26, the third layer ofconductive material 32, the second layer of dielectric material 40, andthe fourth layer of conductive material 42. It should be realized thatin other embodiments of the invention, additional numbers of “vias” 28or 30 may be selectively created and utilized in the foregoing manner.In other non-limiting embodiments, commercially available copper may beelectroplated upon the surface boundaries forming and/or surroundingeach of the apertures or “vias” 28, 30. It should also now be realizedthat, the foregoing etching of layer 42 allows the remaining portions 45of layer 42, which are not connected to material 48, to become and/or tofunction as electrically conductive air bridges or crossover circuits.

[0032] In the eleventh step of process 10, which is best shown in FIG.1(k), a multi-layer circuit board or assembly 64 is created by applyinga conventional acrylic solder masking material 54 to various selectedportions of the created air bridges or crossover circuits 45, 46 inorder to structurally protect the formed air bridges or crossovercircuits 45, 46 from deformation and allowing the formed air bridges orcrossover circuits 45, 46 to accommodate relatively heavy wire bondingmaterial and relatively heavy components. As should be known to those ofordinary skill in the art, material 54 may be applied by a conventionalscreen printing or photo-imaging process.

[0033] It should be realized that the previously delineated process 10allows for the relatively efficient creation of a multi-layer circuitboard and/or assembly 64 which is capable of operatively containing aselected number of electrically conductive layers 14, 16, 32, 42 and aselected number of “grounded” and “non-grounded” “vias” or apertures 28,30 which are formed without drilling. It should be further realized thatthe foregoing process 10 substantially eliminates and/or reduces theneed for costly and time consuming layer alignment procedures and theuse of additional adhesive material due to the partial curing of thedielectric material layers 26, 40. It should also be realized that theforegoing process produces “blind type” apertures 28, 30 which containsubstantially no aluminum material 18, thereby allowing for the relativeefficient flow or use of solder material 48 in these selectivelyextended apertures 28, 30. Moreover, these filled apertures 28, 30cooperate with the various material layers 14, 16, 18, 26, 32, 40, and42 to provide an electrically interconnected circuit board 64 which maybe functionally tested (e.g., solder receiving apertures 28, 30electrically connect the various conducting layers 14, 16, 32, and 42)prior to receiving electrical components. Further, many diverse typesand/or shapes of electrical busses may be formed upon and/or within thecircuit board 64.

[0034] It should be understood that the invention is not limited to theexact embodiment or construction which has been illustrated anddescribed but that various changes may be made without departing fromthe spirit and the scope of the invention.

What is claimed is: 1) A method for making an electric circuit boardcomprising the steps of: providing a member having a central layer of afirst material which is operatively contained between first and secondlayers of a second material; placing a layer of a third material uponcertain portions of said first layer, thereby exposing at least oneportion of said first layer; and placing a plurality of layers of saidsecond material on top of said third layer, effective to form amulti-layer circuit board having an aperture which extends through saidformed circuit board and which terminates upon said exposed at least oneportion of said first layer. 2) The method of claim 1 wherein saidsecond material comprises electrically conductive material. 3) Themethod of claim 2 wherein said second material comprises copper. 4) Themethod of claim 3 wherein said central layer of material comprisesaluminum. 5) The method of claim 4 wherein said third material comprisesa dielectric material. 6) The method of claim 1 further comprising thestep of forming a registration slot within said member. 7) The method ofclaim 6 further comprising the step of forming a sighting window withineach of said plurality of layers of said second material and within saidlayer of said third material. 8) The method of claim 1 furthercomprising the step of selectively etching said central layer, effectiveto form at least one air-bridge. 9) The method of claim 1 furthercomprising the step of placing solder within said aperture. 10) Themethod of claim 1 further comprising the step of preventing said centrallayer from being resident within said aperture. 11) A method for makinga circuit board comprising the steps of: providing a member having acentral layer of a first material which is operatively positionedbetween top and bottom layers of a second material; removing a portionof said first and said second layers, thereby exposing portions of saidcentral layer of said first material; providing a first layer of adielectric material and placing said provided first layer of saiddielectric material onto certain portions of said top layer, therebyoverlaying said exposed portions of said central layer and creatingfirst and second exposed portions of said top layer; providing a thirdlayer of said second material and placing said third layer onto saidfirst layer of said dielectric material and over said first and secondexposed portions of said top layer; removing those portions of saidthird layer which overlay said first and said second exposed portions ofsaid top layer; providing a second layer of said dielectric material andplacing said second layer of said dielectric material onto said thirdlayer after those portions of said third layer which overlay said firstand second exposed portions of said top layer have been removed;providing a fourth layer of said second material and placing said fourthlayer upon said second layer of said dielectric material and over saidfirst and second exposed portions of said top layer; and removing thoseportions of said fourth layer which overlay said first and said secondexposed portions of said top layer, thereby creating an electricalcircuit board having a first aperture which extends through said thirdand fourth layers of said second material and through said first andsecond layers of said dielectric material while terminating within saidfirst layer of said second material, and a second aperture which extendsthrough said third and fourth layers of said second material and throughsaid first and second layers of said dielectric material whileterminating within said first layer of said second material. 12) Themethod of claim 11 wherein said first material comprises aluminum. 13)The method of claim 12 wherein said second material comprises copper.14) The method of claim 11 wherein said first aperture is electricallygrounded. 15) The method of claim 14 wherein said second aperture isisolated from electrical ground. 16) The method of 11 further comprisingthe step of placing solder within said first and second apertures. 17)The method of claim 11 further comprising the step of forming a divingboard over at least one of said first and second apertures. 18) Acircuit assembly made by the process of: providing a core member havinga central layer of a first material which is operatively containedbetween a top and a bottom layer of electrically conductive material;creating an registration slot within said core member; placingdielectric material on certain portions of said top layer, therebyexposing a first and a second portion of said top layer and creating apre-circuit assembly; and using said created registration slot toselectively add layers of electrically conductive material to saidpre-circuit assembly, thereby creating a circuit assembly having a firstaperture which is formed through said created circuit assembly and whichterminates within said first exposed portion and having a secondaperture which is formed through said created circuit assembly and whichterminates within said second exposed portion. 19) The circuit assemblyof claim 18 wherein an alignment slot is formed within each of saidlayers of electrically conductive material. 20) The circuit assembly ofclaim 19 wherein solder is placed within each of said first and secondapertures.